Polycrystalline structure of a chemical vapor deposited (CVD) diamond vacuum window was investigated by means of white-beam diffraction. Forward Laue diffraction patterns were recorded using two-dimensional flat panel sensor. A computer aided approximate indexation of the Laue spots was performed based on maximum correlation between
observed and directly simulated patterns. Different sets of the diffraction patterns were attributed to the different diamond crystalline grains. Retrieved orientations of the illuminated grains were rather random and average linear dimension of the single grain was about 56-64 μm.
We developed ultra-precise fabrication system for x-ray optics, which combined numerically controlled plasma CVM and EEM. In this system, nanometer order form accuracy having atomic order roughness is achieved. And there are no deformed layers on the surface because these fabrication processes utilizes chemical reaction. So, this system is effective for not only reflective optics but also for diffractive optics. Recently, elliptical mirrors having less than 3
nm form accuracy are fabricated by utilizing the above system, and K-B arrangement microfocusing unit for installation of these mirrors are developed. In this unit, micro x-ray beam having the size of 180 (V)×90(H) nm2 is achieved at 15 keV. By scanning irradiation of the micro x-ray beam and by detecting x-ray fluorescence, inside structures of some mammalian cells are observed with resolution of 0.2 μm.
A new figure correction method is applied to fabricate an elliptical mirror to realize a one-dimensionally diverging X-ray beam having high image quality. Mutual relations between figure errors and intensity uniformities of diverging X-ray beams are also investigated using a wave-optical simulator and indicate that figure errors in relatively short spatial wavelength ranges lead to high-contrast interference fringes. By using the microstitching interferometer and elastic emission machining, figure correction of an elliptical mirror with lateral resolution close to 0.1mm was carried out. A one-dimensional diverging X-ray obtained by the fabricated mirror was observed at SPring-8 and evaluated to have a sufficiently flat intensity distribution.
Focusing methods using mirror optics are intensively studied in the field of X-ray microscopy because mirror optics has useful features such as high photon efficiency and no chromatic aberrations. Employing a wave-optical method, we investigated the relationship between the natures of figure errors on the mirror surface and optics performances such as sizes, intensities and satellite peak structures of the focused X-ray beam. We also evaluated uniformity of intensity in the spherically diverging beam from the focal point as a point source. Obtained results showed unprecedented degrees of surface figure accuracy such as higher than 1nm in all over the spatial wavelength range longer than 0.5mm was required to realize nearly diffraction-limited focusing including satellite structures and intensity flatness at the spherically diverging wavefront.
Elliptical mirrors for X-ray microfocusing were manufactured using the new fabrication methods of elastic emission machining (EEM) and plasma chemical vaporization machining (CVM). Surface profiles measured with stitching interferometry showed a maximum deviation around the ideal figure of about 5nm in peak-to-valley. The mirror showed nearly diffraction-limited focusing performance, with a 200 nm line width at the focus. Wave-optical calculation, taking the measured surface profile into consideration, well reproduced the measured focusing properties both at the beam waist and around the beam waist. In addition, two-dimensional focusing unit using K-B mirror arrangement was also developed and evaluated to have about 200 × 200 nm2 focusing performance.
We established an efficient ultra-precision figuring process in which a numerically controlled plasma chemical vaporization machining (NC-PCVM) and a numerically controlled elastic emission machining (NC-EEM) are utilized serially. Intensity images of the X-rays reflected by total reflection mirrors greatly fluctuates with respect to the figure error having spatial wavelength ranging from the submillimeter to 10mm. In the present study, elliptical mirrors for the Kirkpatrick-Baez (K-B) focusing unit was manufactured by NC-PCVM and NC-EEM, and figure accuracy higher than 3nm (p-v) was achieved over the spatial wavelength range longer than 0.5mm. The focusing property was evaluated at the BL29XUL of SPring-8, and spot size of 0.2×0.2 μm2 (FWHM) was realized at 15keV.
Circular and linear zone plates have been fabricated on the surface of silicon crystals for the energy of 8 keV by electron beam lithography and deep ion plasma etching methods. Various variants of compound zone plates with first, second, third diffraction orders have been made. The zone relief height is about 10 mkm, the outermost zone width of the zone plate is 0.4 mkm. The experimental testing of the zone plates has been conducted on SPring-8 and ESRF synchrotron radiation sources. A focused spot size and diffraction efficiency measured by knife-edge scanning are accordingly 0.5 mkm and 39% for the first order circular zone plate.
Plasma CVM (chemical vaporization machining) and EEM (elastic emission machining) systems were developed for coherent X-ray optics fabrication. Figure-correction performances were tested in the spatial wavelength range from submillimeter to several hundreds mm, and those processes were certified to be promising technique to fabricate next-generation mirrors for coherent X-ray beams. A wave-optics simulation code was also developed to feed scientific analysis back to the fabrication technology. A figure measurement technique was also proposed to satisfy the suggestions from the wave-optics simulations. Simulated results indicated the necessity of the figure measurement with subnanometer accuracy having lateral resolution more than submillimeter.
A novel type of micro-pore optics for the X-ray regime has been developed. These optics have a radial design instead of the square packing in the more traditional Lobster-eye optics. With such a design true imaging, without a crucifix in the focus, can be achieved. We demonstrate that the walls inside the square pores are good enough to produce sub- arcminute focussing up to photon energies above 10 keV. The current performance of the optics is limited by large-scale distortions of the plates, probably caused by the method to fuse the fibers together.
Surface flatness of optical elements like mirrors and multilayers may significantly influence on the experiments exploiting coherence properties of x rays. A wavy mirror surface can be considered as a random-phase object. In the article, brief notes on the coherence propagation downstream from a random-phase object are presented. Image formation of a wavy surface at grazing incidence is analyzed. An approach to the inverse problem solution of phase retrieval from the mirror images in coherent x rays is shown. A performed experiment demonstrates general consistency in surface topography obtained by means of x rays and LTP. The estimates on the coherence degradation due to surface roughness are obtained.
Perfect crystals with asymmetric surface cut were studied to evaluate their influence on the coherence of x-rays. An analysis of single- and double-crystal setups in both Bragg and Laue geometries is presented. The Bragg case was studied experimentally. The experiments were performed at Optics Beamline BM5 of the European Synchrotron Radiation Facility. A virtual source created by an asymmetric crystal was probed using an interferometry technique based on fringe analysis, which were produced by boron fiber. The conditions required to preserve coherence in a double-crystal setup are obtained theoretically, and proved experimentally in case of Bragg diffraction.
X-ray optics based on micro-channel plates (MCPs) offer some distinctive advantages over conventional technologies used to produce imagin optics for astrophysics applications. Such micro-pore optics (MPOs) are far lighter and allow a larger stacking density than optics based on metallic foils or plates. Until recent, x-ray optics based on MCPs were not feasible or useful because of the limited quality of the MCPs. We have produced thick square pore MPOs of improved quality and have developed methods to stack the channels in a radial pattern, as required for imagin optics based on Wolter type I or II designs. The individual plates were tested in synchrotron radiation facilities and conventional beam lines to determine their geometric and surface scattering properties.
We have performed x-ray specular reflectivity and scattering measurements of thermally slumped glass substrates on x-ray diffractometers utilizing a rotating anode x-ray source at the Danish Space Research Institute (DSRI) and synchrotron radiation at the European Synchrotron Radiation Facility (ESRF) optics Bending Magnet beamline. In addition, we tested depth graded W/Si multilayer-coated slumped glass using x-ray specular reflectivity measurements at 8.048 keV and 28 keV and energy-dispersive measurements in the 20-50 keV rang at a double-axis diffractometer at the Orsted Laboratory, University of Copenhagen. The thermally slumped glass substrates will be used to fabricate the hard x-ray grazing incidence optics for the High-Energy Focusing Telescope. We compared the measurements to the SODART- mirrors from the SRG telescope mission program. The surface scatter measurement of the thermally slumped glass substrates yields Half Power Diameters (HPD's) of single- bounce mirrors of full-illuminated lengths of approximately 40 arcseconds for typical substrates and as low as approximately 10 arcseconds for the best substrates, whereas the SODART mirrors yields HPD's of approximately 80 arcseconds with very little variation. Both free-standing glass substrates and prototype mounted and multilayer-coated optics were tested. The result demonstrate that the surface scatter contribution, plus any contribution from the mounting procedure, to the Half Power Diameter from a telescope using the slumped glass optics will be in the subarcminute range.In addition we measured low surface microroughness, yielding high reflectivity, from the glass substrates, as well as from the depth graded W/Si multilayer-coated glass.
Focusing of hard X-rays by refraction has been a long time been considered as unfeasible due to strong absorption and weak refraction of X-rays in matter. Recently it has been shown that compound refractive lenses can overcome the problem. It was demonstrated that the best candidates for lenses are low Z, high density materials. Linear and 2D lenses from aluminum, boron carbide, beryllium, pyrographite and Teflon were produced and tested. Focusing of 2 - 3 microns was achieved at an energy range from 9 to 30 keV. Compound refractive lenses have low sensitivity to heatload and are extremely well suited for focusing of undulator radiation. Two-plane focusing lenses have been optimized, built and installed in the white beam of the undulator on the machine diagnostic beamline of the ESRF to be used as an X-ray emittance diagnostic. The future potentials of the refractive lenses will be discussed as well.
The performance of a fixed exit double crystal monochromator in terms of stability and reproducibility of the outgoing X- ray beam becomes the crucial point at modern synchrotron beamlines dealt with the high resolution X-ray optics. Due to the high heat load the monochromator crystals have to be cryogenically cooled. The cooling loop of the second crystal may have an impact on the performance of the monochromator. We therefore suggest to use a Si1-xGex single crystal as the first cooled crystal of the monochromator. With that the second crystal is held at room temperature. To verify the proposed solution an experiment was performed where the lattice parameters of pure Si and SiGe crystals as a function of temperature were measured.
It is shown that the x-ray mirrors which have been made on the verge of potentialities of the modern technology, give rise to deterioration of the coherent properties of the beam delivered by the third generation synchrotron radiation sources. In other words mirrors produce speckle structure in the reflected x-ray beam. The theoretical analysis of partially coherent x- ray beam scattered by moderately rough mirror surface under the total reflection condition is presented and the estimates for the intensity contrast as a function of the surface parameters are given. The observed speckle structure was experimentally recorded by means of high resolution photo film. It is shown that the polishing process must be significantly improved in the case of the long mirrors (approximately 1 m) used as the standard optical elements at the beamlines, while small mirrors (less than 0.2 m) are in a better state and may be applied to various imaging techniques exploiting coherent x-ray properties.
We present the x-ray performance on an ESRF synchrotron beamline of a focusing device based on the dynamical bending of a flat silicon plate coated with a 2.5 m d-spacing W/Si multilayer. The mirror was shaped by trial and error to a cylindrical ellipse using an optical profilometer. In a first experiment the device was bent to a 71-m radius to account for the demagnification factor and the energy of operation. With a monochromatic incident beam set at 9 keV a vertical spot size of 4.5 micrometers was obtained at 41 m from the source and 1 m from the multilayer, which agreed closely with theoretical expectations. Such good agreement was due to small residual slope error with respect to the ellipse: around 2 (mu) rad over a 150-mm length for radii greater than 50 m. Moreover, as the divergence of the incident beam was larger than the rocking curve width, less than 25% of the mirror could contribute, reducing the distortion to an even lower figure. With the same geometrical parameters the device exposed to the white beam (monochromator removed) lead to a vertical spot size of about 7 micrometers . Here the whole mirror surface cold reflect, which caused more distortion to the incoming beam but also gave rise to a much higher intensity. The gain in flux obtained with a gradient of d-spacing along the mirror surface is discussed. Finally, results with a Kirpatrick-Baez arrangement let expect in the near future a flux gain greater than 104 with a 10 micrometers by 10 micrometers focal spot.
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